A syringe is generally composed of an outer tube provided on the tip end side thereof with a mouth portion reduced in diameter, a gasket inserted in the outer tube via a base end opening of the outer tube, and a pusher (plunger rod) connected to the gasket.
A prefilled syringe with a chemical preliminarily contained (sealed) in a syringe is known. The chemical usually is aseptically sealed in a space (first space) on the tip end side relative to the gasket maintained in a hermetically closed condition by a seal at the mouth portion. In using the prefilled syringe containing a liquid chemical as a chemical, for example, the outer tube is usually held by one hand, and the pusher is pushed by the other hand to slide the gasket in the outer tube to the tip end direction, thereby discharging (injecting) the liquid chemical via the mouth portion. Besides, where the chemical is a powdery chemical, usually, the pusher is once pulled to slide the gasket to the base end direction, and a liquid such as an injection is sucked into the first space via the mouth portion of the outer tube, thereby dissolving the chemical to form a liquid chemical, and the pusher is then pushed so as to discharge the liquid chemical.
The pusher of a commercially available syringe (prefilled syringe) generally has a main body portion having a cross section shaped like a cross, with tip end portions of the cross abutting on the inside wall of the outer tube. Therefore, the gap (second space) between the outer tube inside wall and the pusher on the base end side relative to the gasket is in an open condition and, when the open condition is kept as it is, foreign matter such as dirt and dust may enter into the second space together with the outside air or bacterial pollution may occur during storage, transportation or the like, which is disadvantageous on a sanitary basis. Therefore, the syringe is usually shipped as a product aseptically packaged with a packaging material.
In using such a packaged syringe, the space in the outer tube on the tip end side relative to the gasket is maintained in the aseptic hermetically closed condition until a mouth portion seal is unsealed even after the packaging material is opened, whereas the outside air flows into the space on the base end side relative to the gasket simultaneously when the packaging material is opened.
In view of this, a syringe with a cap attached to the base end of the non-used syringe is also known. For example, in a prefilled syringe proposed in Japanese Patent Laid-open No. Hei 7-246238 wherein a medical drug and a diluting liquid are sealed respectively in an outer tube and an inner tube (piston rod) and individually stored there, the base ends of the outer tube and the inner tube are sealed with caps, respectively. This configuration ensures that, when not in use during storage or transportation, the outside air is blocked from flowing into the spaces in the outer tube and the inner tube on the base end side relative to the piston (gasket).
However, the prefilled syringe of the type in which the outer tube and the inner tube are individually sealed with caps has the disadvantage that the operation at the time of using it is intricate and troublesome, since an operation of removing the caps is needed and it is necessary to attach an inner tube tip end portion to the piston in the outer tube and to attach another pushing rod (pusher) to a base end portion of the inner tube (see FIG. 2 of the above-mentioned publication). In order to improve the intricateness at the time of use, i.e., removal of the caps and attachment of the pusher, it may be contemplated to provide each of the caps for the outer tube and the inner tube with a hole and to insert the inner tube and the pusher into the holes in a gas-tight condition, thereby integrating the prefilled syringe.
However, the gas-tight sealing on the base end side of the outer tube as above-mentioned makes it difficult to push the pusher for discharging the liquid. This is because the pressure inside the space in the outer tube on the base end side relative to the gasket is lowered, attendant on the operation to push the pusher for sliding the gasket inside the outer tube to the tip end direction so as to discharge or inject the liquid, with the result that a force for pushing back the gasket (pusher) to the base end direction is exerted.
In addition, the syringe is shipped in the state of being packaged as above-mentioned, so that, when the pusher is pushed by some force and the gasket is thereby moved inside the outer tube to the tip end direction during transportation or storage, the following troubles are generated.
1) By being pushed by the gasket moved, a cake (a certain-shaped freeze-dried preparation) of a chemical may be collapsed, thereby spoiling the beautiful appearance of the product.
2) Due to the movement of the gasket to the tip end direction, the collapsed powdery chemical (or a chemical being in a powdery form from the beginning) may enter into the gap between the outer circumferential surface of the gasket and the inner circumferential surface of the outer tube. If the chemical has entered into the gap, at the time of feeding the chemical by use of the syringe, the chemical having entered into the gap may be left undissolved in the liquid sucked into the outer tube, causing an error in the amount of the chemical fed.
3) Where the presealed chemical is a liquid (liquid chemical), when the gasket is going to move to the tip end direction, the pressure of the liquid chemical is increased, with the result that the liquid may leak out by breaking the sealing member at the mouth portion or may leak to the base end side of the gasket via the gap between the outer circumferential surface of the gasket and the inner circumferential surface of the outer tube.